Ultra-high strength maraging stainless steel with salt-water corrosion resistance

Patent metadata

Field	Value
Publication number	US-11085093-B2
Application number	US-201716315475-A
Country	US
Kind code	B2
Filing date	Jul 5, 2017
Priority date	Jul 26, 2016
Publication date	Aug 10, 2021
Grant date	Aug 10, 2021

Abstract

An ultra-high strength maraging stainless steel with nominal composition (in mass) of C≤0.03%, Cr: 13.0-14.0%, Ni: 5.5-7.0%, Co: 5.5-7.5%, Mo: 3.0-5.0%, Ti: 1.9-2.5%, Si: ≤0.1%, Mn: ≤0.1%, P: ≤0.01%, S: ≤0.01%, and Fe: balance. The developed ultra-high strength maraging stainless steel combines ultra-high strength (with σb≥2000 MPa, σ0.2≥1700 MPa, δ≥8% and ψ≥40%), high toughness (KIC≥83 MPa·m½) and superior salt-water corrosion resistance (with pitting potential Epit≥0.15 (vs SCE)). Therefore, this steel is suitable to make structural parts that are used in harsh corrosive environments like marine environment containing chloride ions, etc.

First claim

What is claimed is:

1. A maraging stainless steel comprising:
13 to 14 wt % chromium (Cr);
5.5 to 7.0 wt % nickel (Ni);
5.5 to 7.5 wt % cobalt (Co);
3 to 5 wt % molybdenum (Mo);
2.2 to 2.5 wt % titanium (Ti);
at most 0.03 wt % carbon (C); and
iron (Fe),
wherein the maraging stainless steel is prepared by melting and casting.

2. The maraging stainless steel of claim 1 having a silicon (Si) content of at most 0.1 wt %.

3. The maraging stainless steel of claim 1 having a manganese (Mn) content of at most 0.1 wt %.

4. The maraging stainless steel of claim 1 having a phosphorus (P) content of at most 0.01 wt %.

5. The maraging stainless steel of claim 1 having a sulfur (S) content of at most 0.01 wt %.

6. The maraging stainless steel of claim 1 having:
a silicon (Si) content of at most 0.1 wt %;
a manganese (Mn) content of at most 0.1 wt %;
a phosphorus (P) content of at most 0.01 wt %; and
a sulfur (S) content of at most 0.01 wt %.

7. The maraging stainless steel of claim 1 wherein said chromium is present at 13.0 to 13.1 wt %.

8. The maraging stainless steel of claim 1 wherein said nickel is present at 6.9 to 7.0 wt %.

9. The maraging stainless steel of claim 1 wherein said cobalt is present at 5.5 to 5.6 wt %.

10. The maraging stainless steel of claim 1 wherein said molybdenum is present at 3.4 to 3.5 wt %.

11. The maraging stainless steel of claim 1 wherein said titanium is present at 2.3 to 2.5 wt %.

12. The maraging stainless steel of claim 1 wherein said titanium is present at 2.4 to 2.5 wt %.

13. The maraging stainless steel of claim 1 wherein:
said chromium is present at 13.0 to 13.1 wt %;
said nickel is present at 6.9 to 7.0 wt %;
said cobalt is present at 5.5 to 5.6 wt %; and
said molybdenum is present at 3.4 to 3.5 wt %.

14. The maraging stainless steel of claim 1 further comprising:
at most 0.1 wt % silicon;
at most 0.1 wt % manganese;
at most 0.01 wt % phosphorus; and
at most 0.01 wt % sulfur.

15. A maraging stainless steel comprising:
13 to 14 wt % chromium (Cr);
5.5 to 7.0 wt % nickel (Ni);
5.5 to 7.5 wt % cobalt (Co);
3 to 5 wt % molybdenum (Mo);
2.2 to 2.5 wt % titanium (Ti);
at most 0.03 wt % carbon (C); and
iron (Fe),
wherein the maraging stainless steel is prepared by melting and casting, and
wherein the maraging stainless steel has ultra-high strength represented by ab 2000 MPa, has high ductility represented by δ≥8%, and has salt-water corrosion resistance represented by pitting potential Epit≥0.15 (vs SCE).

16. A method for heat processing the maraging stainless steel of claim 1 , the method comprising:
forging the maraging stainless steel in austenite phase region, with a forging ratio of 6-9, and air cooling to room temperature after forging; and hot-rolling the maraging stainless steel after forging, with a starting temperature of 1150-1250 ° C., and a finishing temperature of at least 900 ° C., and air cooling after hot-rolling.

17. The method of claim 16 wherein the forging ratio is greater than 8.

18. The method of claim 16 wherein an accumulated rolling reduction during the hot-rolling is at least 80 percent.

19. A method for heat treating the maraging stainless steel of claim 1 , the method comprising:
solution treatment of the maraging stainless steel at 1050-1150 ° C. for 1-2 h, and then air cooling to room temperature;
after the solution treatment, cryogenic treatment of the maraging stainless steel in liquid nitrogen (−196 ° C.) for at least 5 h; and after the cryogenic treatment, aging treatment of the maraging stainless steel at 450-520 ° C. for 30 min to 16 h, followed by air cooling.

20. The method of claim 19 wherein:
the solution treatment is performed at 1100 ° C. for 1.5 h;
the cryogenic treatment is performed for at least 10 h; and
the aging treatment is performed at 480 ° C. for 10 h.

Assignees

• Boeing Co
• Institute Of Metal Res

Inventors

• Tian Jialong
• Yang Ke
• Wang Wei
• Shan Yiyin
• Yan Wei

Classifications

• C21D8/00 Primary

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• C21D1/18 Primary

  Hardening (C21D1/02 takes precedence); Quenching with or without subsequent tempering (quenching devices C21D1/62) · CPC title

• C21D6/005

  containing Mn · CPC title

• C22C38/44

  with molybdenum or tungsten · CPC title

• C22C38/52 Primary

  with cobalt · CPC title